Hovis has launched an investigation into claims that workers at one of its manufacturing sites were under the influence of alcohol or drugs on-site.

Scottish television channel STV reported that four employees at the Duke Street-based Glasgow bakery were sacked after taking drug tests and another nine workers resigned on the spot when bosses announced that all staff would be tested.

The bakery giant, which employs 338 people at the Scottish factory, refused to confirm the number of employees involved or provide details of the incident when approached by British Baker.

“At Hovis, we have a zero tolerance policy for alcohol or substance use during working hours,” the company’s statement said.

“It was bought to our attention that a very small number of employees at our Glasgow bakery may be under the influence of alcohol or drugs while at work. We are continuing to investigate these claims.”